1. Field of the Invention
The present invention relates to an optical disc reproducing apparatus, which detects binary data from analog signals obtained from an optical disc under various kinds of optical disc environments including a high-density disc environment such as 15 GB in a 12 cm diameter disc by supporting Run Length Limited (RLL)(1,10) and RLL(2,10) codes, a 5-tap partial response maximum likelihood (PRML) sixteen levels, an asymmetric compensating operation under such RLL code environments, and a minimum T signal compensating operation.
2. Description of the Related Art
With the onset of the multimedia era, the need for storing and transmitting a large quantity of digital data has increased. Accordingly, an optical disc such as a digital video disc (DVD) has been widely studied in the art. The current DVD market is steadily growing, being divided into a computer industry that desires to adopt a DVD-ROM and a home appliance industry that intends to promote a DVD-video. Additionally, the DVD extends an applicable sphere as a DVD-R (recordable), a DVD-RW (rewritable), and a DVD-RAM (random access memory) appear on the market.
Such kinds of conventional optical discs may often be confronted with various problems as follows. When data stored in the optical disc are reproduced, analog radio frequency (RF) signals under reproduction may frequently exhibit an asymmetric waveform. Furthermore, this asymmetric phenomenon may give rise to other unfavorable phenomena such as jitter, non-linear bit transition, DC transition, and inter-symbol interference (ISI) between symbols of reproduced data. Such phenomena may make it difficult to execute the detection and correction of frequency errors and phase errors, thus causing the distortion of reproduced signals. A conventional optical disc reproducing apparatus has typically used a digital sum value (DSV) algorithm to correct such asymmetric errors.
However, the conventional DSV algorithm does not always execute an exact correction of the asymmetric errors under various code environments such as RLL(1,10) and RLL(2,10). For example, the conventional DSV algorithm may often fail to exactly detect asymmetric errors in the case of 4T sampling signals reproduced in the variable frequency oscillator (VFO) sector of the optical disc.
Furthermore, the conventional optical disc reproducing apparatus does not support an integrated solution for both RLL(1,10) and RLL(2,10) codes. Therefore, two separate and independent code detectors, namely, adding an RLL(1,10) detector to an existing RLL(2,10) detector, are used to support the integrated solution. This configuration of the detectors may, however, be inefficient in circuit area use and power consumption.
Additionally, a 4-Tap partial response maximum likelihood (PRML) structure of the conventional optical disc reproducing apparatus may fail to execute the optical disc reproduction under a high-density environment of more than 15 GB in a 12 cm diameter disc.
Additionally, a frequency detector of the conventional optical disc reproducing apparatus may fail to effectively detect frequency errors under such a high-density environment with a frequent ISI and a high noise. Also, a delay in frequency locking timing may interrupt a stable phase locked loop (PLL) operation.
Additionally, an asymmetry compensator of the conventional optical disc reproducing apparatus may be unavailable for some optical discs such as DVD-RAM, thus putting restrictions on reproducible kinds of the optical disc.
Additionally, the above-mentioned detector of the conventional optical disc reproducing apparatus requires a high-priced external measurer to measure a signal quality, therefore, actual measurement of the signal quality is not simple.
Additionally, a minimum T compensator of the conventional optical disc reproducing apparatus may be not operable under an RLL(1,10) code environment.
To overcome the above-discussed problems, an improved optical disc reproducing apparatus capable of operating under various disc environments and capable of executing an exact and effective reproduction under a high-density environment with a frequent ISI and a high noise is required in the art.